1. Field of the Invention
This invention relates to an image information input system, and more particularly relates to a system for inputting image brightness information into an exposure control system for use in a photographic camera or a photographic printer in which various parts of an image are differently weighted for providing modified image information according to the kind of the scene of the image.
2. Description of the Prior Art
There have been known various kinds of light measuring systems such as averaged light measuring, center-weighted measuring system and partial measuring. In the averaged light measuring, the averaged value of the amount of light from the whole scene viewed by the taking lens of the camera is measured by use of a photodetector which has substantially the same angle of view as that of the taking lens. In this light measuring system, it is impossible to obtain a proper exposure of the subject matter to be photographed when there is a bright background behind the subject matter such as the sky or source of back light. Though it is known to correct the exposure controlled by the averaged light measuring system by use of a correction means which effects increase or decrease of the measured values, it is troublesome to operate such a correcting means and it is difficult to accurately correct the exposure by the optimum amount.
In the center-weighted measuring, the central part of an image is weighted in comparison with the marginal part. In the partial measuring, only a part of an image is measured. These two light measuring systems are based on an empirical rule that the subject matter of photography is normally located around the center of the scene aimed by a camera and weights the central part in comparison with the marginal part to lower the weight of the brightness information of the marginal part of a scene. Accordingly, these two light measuring systems are disadvantageous in that the exposure cannot be properly controlled based thereon if the subject matter is not located around the center of a scene or if the difference in brightness between the central part and the marginal part is too large.
Beside the above mentioned light measuring systems, there have been known in the art to use the maximum and minimum values of the brightness of some parts of a scene to obtain more practical information as disclosed in Japanese Unexamined Patent Publication Nos. 92622/1976, 13412/1978, 91224/1979 and Japanese Utility Model Publication No. 9271/1976, and to divide the scene into the upper half and the lower half to obtain information of these halves separately as disclosed in Japanese Unexamined Patent Publication Nos. 75422/1976, 96829/1978, 90926/1974, 90927/1974, 71834/1978, 118127/1978 and Japanese Patent Publication No. 8516/1971.
The scene or subject matter to be photographed or printed can be roughly classified into either a back light scene and a normal light scene. The deviation of the average brightness from the brightness of the subject matter is much different between the back light scene and the normal light scene. Therefore, it is necessary to make much different exposure between the two kinds of scene.
The above-mentioned various kinds of light measuring systems, however, are all disadvantageous in that it is very difficult to provide optimum light measuring or optimum image information for both kinds of the scene. More particularly, the above systems are effective for the normal light scenes but not for the back light scenes, because the photodetectors and the processing circuit are always of the same type for both kinds of scenes.